General properties of antimony microelectrode in comparison with glass microelectrode for pH measurement

Two kinds of pH-sensitive microelectrodes were constructed: 1) glass microelectrode with a pH-sensitive tip of 50--100 micrometers in length, and 2) antimony (Sb) microelectrode with a tip of 1--5 micrometers in outside diameter. Comparisons of the two were made on the change in the electromotive force (EMF) in response to various pHs and biological applicability. The pH sensitivity (slope constant) at 20 degrees C of the glass and Sb-microelectrodes averaged 51.7 and 51.9 (-mV/pH), respectively. Over the pH range of 2 to 9, both electrodes responded linearly to the change of pH. The pH-dependent EMF of the Sb-microelectrode was influenced by phosphate buffers, but not by Tris-HCl buffers. Through the glass microelectrode showed a linear response to all the buffers tested, its slope constant tended to be limited by the surface area of the pH-sensitive tip. The stability of the EMFs was well within 1 mV for 12 hr with the glass microelectrode but more than 10 mV with the Sb-microelectrode. One the other hand, the 95% response time was about 1 min with the glass microelectrode, whereas it was less than a few seconds with the Sb-microelectrode. Blood pH was measured with the two electrodes and reasonable values were obtained with both methods, although the values by use of the Sb-microelectrode were slightly higher than those of the other. In view of the practical ease of manufacturing, maintenance and durability, the use of the Sb-microelectrode in biological measurement should also be re-evaluated, but several restrictions must be imposed on it.